1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus and, more particularly, to a photoelectric conversion apparatus which is used as an image information input means such as a scanner, a digital copier, or the like and in which pixels, each pixel being constructed using a photoelectric conversion element and a switching element, are arrayed one-dimensionally or two-dimensionally, and an image pickup apparatus using it.
2. Related Background Art
Reading systems making use of a demagnifying optical system and a CCD sensor have been used heretofore as information reading systems (image information input means) of facsimile devices, digital copiers, X-ray image pickup apparatus, etc.; or popularly utilized image reading devices are those provided with a reading system having photoelectric conversion elements using a photoelectric conversion semiconductor material typified by hydrogenated amorphous silicon (hereinafter referred to as axe2x80x94Si), and switching elements.
Particularly, axe2x80x94Si can be formed uniformly and at low temperature over a substrate of a large area. This presents the advantage of capability of being formed on an inexpensive glass substrate, and it is thus applied widely.
It is known that pin photodiodes can be used for the photoelectric conversion elements of the photoelectric conversion apparatus described above and TFTs can be suitably applicable to the switching elements.
For example, ""94 SPIE Vol. 2127, P144-P151 describes that the photoelectric conversion apparatus is sensitive to even weak light and the dynamic range (DR) achieved is 104 to 105. It is, however, described that DR is greatly affected by noise such as random noise, thermal noise, and the like. Further, ""97 SPIE Vol. 3032, P2-P13 introduces an X-ray digital detector as an application example of the photoelectric conversion apparatus of this type.
The X-ray digital detector is equipped with a fluorescent substance such as CsI or the like or a fluorescent sheet such as Gd2O2S or the like for converting an X-ray image to a visible image, and the photoelectric conversion apparatus for receiving light emitted from the fluorescent sheet.
FIG. 1 is a schematic, equivalent circuit diagram for explaining an example of the X-ray digital detector. FIG. 2 is a schematic plan view of one pixel in the photoelectric conversion apparatus forming the X-ray digital detector and FIG. 3 a schematic crosssectional view thereof. A driver 1 of FIG. 1 is connected via gate lines 2 to TFTs 3 as switches. Radiated X-rays are converted into light in a sensitive wavelength region by the fluorescent sheet placed on pin photodiodes 4 as photoelectric conversion elements, and the light is incident to the pin photodiodes 4, as illustrated in FIG. 3.
The light incident to each photodiode 4 travels through a transparent electrode 9 and further undergoes photoelectric conversion in a semiconductor layer 10; more specifically, the light travels, for example, through a p-type layer and then undergoes the photoelectric conversion in an i-type axe2x80x94Si layer; whereby the light signal is converted into an electric signal. The charge resulting from the photoelectric conversion is stored in the photodiode 4.
Charges stored in the respective photodiodes 4 are outputted via signal lines 5 to an amplifier 7 by successively turning the TFTs 3 on by a control signal from the driver 1. Then the amplifier 7 amplifies the electric signals and an A/D converter 8 executes A/D conversion thereof to output digital signals to a computer or the like not illustrated. A backward bias is applied through bias line 6 to the photodiodes 4.
The computer carries out image processing to display the input image signals on a monitor or the like or to record the data in a recording medium or the like.
Incidentally, there are strong desires for increase in the photosensitivity of the photodiodes in the photoelectric conversion apparatus as described above. Particularly, in the case of the X-ray image pickup apparatus, the increase of sensitivity directly results in the significant advantage of capability of decreasing an X-ray dose, and is thus a challenge to be solved soon. FIG. 4 shows an example of the relationship between quantity of light received by the photodiodes and output of electric signal from the sensors. This figure shows the sensors that can be used in the range of light quantity of 10xe2x88x923 to 1, and the demand is to make them able to be used, for example, in the range of 10xe2x88x924 to 1.
In order to enhance the photosensitivity of the photodiodes, a variety of studies have been made, including increasing an aperture rate of pixels, suppressing noise components in the electric signals by decreasing wiring capacitance, and so on.
There was, however, a limit to increasing the aperture rate of pixels, because the size of the TFTs was determined in consideration of their transfer performance of stored charges. Since the area of crossing portions between the gate line and the signal lines was determined in consideration of the production yield etc., there was also a limit to decreasing the wire-to-wire capacitance by decreasing the wiring width.
An object of the present invention is to enhance the photosensitivity of the photodiodes.
Another object of the present invention is to provide a photoelectric conversion apparatus comprising a plurality of photoelectric conversion elements, a plurality of switching elements connected to said respective photoelectric conversion elements, a plurality of signal lines for outputting electric signals resulting from photoelectric conversion in each of said photoelectric conversion elements, and a plurality of driving wires for driving said photoelectric conversion elements, wherein each of said driving wires is arranged in parallel to said signal lines and between said signal lines and wherein each of said driving wires is located so that a center line thereof lies between a first position, which is a center between said signal lines, and a second position, which is a center of gravity of an area of said photoelectric conversion element.
Another object of the present invention is to provide an image pickup apparatus comprising: a photoelectric conversion apparatus comprising a plurality of photoelectric conversion elements, a plurality of switching elements connected to said respective photoelectric conversion elements, a plurality of signal lines for outputting electric signals resulting from photoelectric conversion in each of said photoelectric conversion elements, and a plurality of driving wires for driving said photoelectric conversion elements; and wavelength conversion means placed on the light incidence side of said photoelectric conversion apparatus, for effecting conversion of incident wavelength and putting light resulting from the wavelength conversion into said photoelectric conversion apparatus, wherein each of said driving wires is arranged in parallel to said signal lines and between said signal lines and wherein each of said driving wires is located so that a center line thereof lies between a first position, which is a center between said signal lines, and a second position, which is a center of gravity of an area of said photoelectric conversion element.
Still another object of the present invention is to provide a photoelectric conversion apparatus comprising a plurality of photoelectric conversion elements arrayed in a matrix of rows and columns, each of said photoelectric conversion elements having a transparent electrode disposed on the light incidence side and an electrode opposed to said transparent electrode through a semiconductor layer, first conductive lines connected to the transparent electrodes and disposed along the rows or the columns of the photoelectric conversion elements, and a plurality of second conductive lines provided adjacent to the photoelectric conversion elements and along the first conductive lines, wherein each of the first conductive lines lies between a first position passing through a center between the second conductive lines and in parallel to the second conductive lines and a second position passing through a center of gravity of a light receiving area of the photoelectric conversion element and in parallel to the second conductive lines.
Still another object of the present invention is to provide an image pickup apparatus comprising: a photoelectric conversion apparatus comprising a plurality of photoelectric conversion elements arrayed in a matrix of rows and columns, each of said photoelectric conversion elements having a transparent electrode disposed on the light incidence side and an electrode opposed to said transparent electrode through a semiconductor layer, first conductive lines connected to the transparent electrodes and disposed along the rows or the columns of the photoelectric conversion elements, and a plurality of second conductive lines provided adjacent to the photoelectric conversion elements and along the first conductive lines, wherein each of the first conductive lines lies between a first position passing through a center between the second conductive lines and in parallel to the second conductive lines and a second position passing through a center of gravity of a light receiving area of the photoelectric conversion element and in parallel to the second conductive lines; and a wavelength conversion element for effecting wavelength conversion of an image-information-carrying signal put into each of the photoelectric conversion elements.
In the present invention the thickness of the transparent electrode or the area of the transparent electrode can be made smaller by properly setting arrangement of the bias wire, whereby the photosensitivity of the sensor is enhanced.
As illustrated in FIG. 2 and FIG. 3, the bias line 6 for applying the bias to the photodiode 4 is provided on the transparent electrode 9 located on the pin photodiode 4. However, the position of the bias line 6 can be anywhere on the transparent electrode 9, and it was not specified particularly.
The present invention is based on such a finding that the sensitivity of photodiodes can be enhanced by giving consideration to the placement location of the bias line 6 (driving line).
Namely, the photosensitivity can be enhanced by optimizing the placement of the driving line, without any substantial change in the layer structure itself of the elements.
The optimization of placement of the driving line permits the uniform bias to be applied to the photoelectric conversion elements. This in turn permits decrease in the thickness of the transparent electrode, so as to decrease an amount of transparent electrode""s absorption of light incident to the photoelectric conversion element, thus increasing the utilization efficiency of light. This can increase the photosensitivity of the photoelectric conversion elements.
The recognition of the importance of placement of the driving line leads to adequate control of the position of the driving line in each element, which decreases variations in characteristics among the elements. The present invention can thus provide the photoelectric conversion apparatus with excellent characteristics. This can then improve the total performance of the image pickup apparatus having the photoelectric conversion apparatus, such as the X-ray image pickup apparatus or the like.